#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h> //POSIX标准定义的unix类系统定义符号常量的头文件
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 30

void error_handling(char* message);

int main(int argc, char* argv[])
{
    int sock;
    char message[BUF_SIZE];
    int str_len;
    socklen_t adr_sz;
    struct sockaddr_in serv_adr, from_adr;

    if(argc != 3)
    {
        printf("Usage : %s <port><ip> \n", argv[0]);
        exit(1);
    }

    sock = socket(PF_INET, SOCK_DGRAM, 0);
        if(sock == -1)
        error_handling("socket() error\n");

    memset(&serv_adr, 0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_adr.sin_port = htons(atoi(argv[2]));

    while(1)
    {
        fputs("Input message(Q to quit) : ", stdout);
        fgets(message, BUF_SIZE, stdin);
        if(!strcmp(message, "q\n") || !strcmp(message, "Q\n"))//相同时返回0
            break;
        
        sendto(sock, message, strlen(message), 0, (struct sockaddr*)&serv_adr, sizeof(serv_adr));
        
        adr_sz = sizeof(from_adr);
        //接收的主机的信息会保存在from_adr中
        str_len = recvfrom(sock, message, BUF_SIZE - 1, 0, (struct sockaddr*)&from_adr, &adr_sz);
        message[str_len] = 0;
        printf("message from server : %s \n", message);
    }
    close(sock);
    return 0;
}

void error_handling(char* message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(-1);
}
